The Center for Gene-Environment studies in Parkinson disease at UCLA (UCLA-CGEP) will bridge three major NIH and VA-supported awards in Parkinson's disease (PD) and one NIH-sponsored study of Huntington's disease. The central hypothesis of the proposed UCLA-CGEP is that gene and environmental toxins combine to increase the risk for PD in susceptible individuals through an interplay between pesticides and mechanisms regulating dopamine homeostasis. We postulate that critical factors in this interaction are oxidative stress and resulting alterations in proteasomal function. Project I "Environmental toxins and genes that influence dopamine in Drosophila and humans" will examine interindividual variability of dopamine vesicular transporter (VMAT) expression due to promoter variants in two human populations in parallel with a reporter gene assay. These populations will be genotyped for functional VMAT2 variants and association analyses of gene-environment interactions and pesticide exposures collected in the parent grant will be conducted. In addition, Drosophila genetics will be used to determine how the expression of VMAT affects dopamine-mediated toxicity and identify genes that modulate VMAT function, which will then be examined in the human population for their relevance to increased risk of PD. Project II "Interaction between pesticides and genetic alterations in dopamine homeostasis in mice" will test the hypothesis that pesticides and genetic variations in combination increase the vulnerability of dopaminergic neurons, and that one of the mechanisms involved is oxidative stress. Genetically engineered mice with a reduction in expression of VMAT or the cytoplasmic dopamine transporters, and mice with altered expression of alpha-synuclein and parkin, two proteins known to cause familial PD, will be examined. Behavior and quantitative anatomy will be used to assess the effect of pesticides on dopaminergic neurons in these genetically altered mice. Histology, gene expression profiling, in vivo neurochemistry and slice electrophysiology will be used to examine the role of oxidative stress in this interaction. Project III, "Pesticides and Proteasomal Dysfunction: genetic susceptibility in cellular models" will test the hypothesis that proteasomal dysfunction is central to the deleterious effects of the combined environmental and genetic insults. Cell lines, primary neuronal cultures from genetically altered mice, and human lymphoblasts will be examined.